The present invention relates to photolithography, and in particular to methods and apparatus for ensuring proper handling of reticles in photolithography systems.
The manufacture of certain types of microdevices, such as semiconductor integrated circuits, flat-panel displays, ink-jet heads and the like, involves the process of photolithography and hence the use of photolithography systems, also called xe2x80x9cphotolithography tools.xe2x80x9d Photolithography tools are designed to project an image of a finely patterned mask (xe2x80x9creticlexe2x80x9d) onto a photosensitive substrate. The reticle typically includes a pellicle, which is a thin membrane displaced from the patterned side of the reticle by a frame. The pellicle serves to keep dust and other particulates off of the patterned surface that would otherwise be imaged onto the substrate. After the substrate is exposed, it is processed to create a desired structure based on the imaged pattern.
The manufacturing process typically involves repeating the photolithography and process steps using different reticles in order to build up the device. Accordingly, photolithography tools typically include (or are operatively coupled with) an automatic reticle handling system to facilitate the rapid loading and unloading of reticles to and from the tool.
Reticles are fragile and thus are always contained inside a protective plastic case called a xe2x80x9ccassettexe2x80x9d until extracted by the reticle handling system. In the reticle handling operation, multiple reticles in their respective cassettes are manually loaded into a reticle library within the photolithography tool. A first reticle handler then inserts a reticle handling arm into a particular cassette to engage the reticle therein. Once engaged, the reticle is then transferred to a second reticle handler, which aligns and delivers the reticle to another location, such as a reticle stage or a pellicle inspection station (e.g., a pellicle particle detector or xe2x80x9cPPDxe2x80x9d) within the photolithography tool.
In many photolithography tools, successful transfer of a reticle from the cassette into its proper position in the tool requires that the reticle be properly positioned on the first reticle handler. Otherwise, the transfer (xe2x80x9chandoffxe2x80x9d) between the first and second reticle handlers can be faulty.
FIG. 1 illustrates a prior art reticle handling system that includes a reticle handling arm 2 that is part of a first reticle handler. The reticle handling arm is in communication with a reticle carrier 4 that is part of a second reticle handler. Reticle carrier 4 includes translatable lifting brackets 6 that are adapted to engage a reticle 8 residing on reticle arm 2 and to lift the reticle from the reticle handling arm.
If the reticle is not properly positioned on the reticle handling arm, the lifting brackets can jam against the reticle, as shown, when attempting to engage the reticle. This can damage the reticle and/or the reticle handling arm, and/or can jam the reticle handling system, thereby causing a system failure.
The consequences of faulty reticle handling can be financially serious. A jammed reticle stops production, requires expert man-hours to repair, and can damage the reticle handling system and/or the reticle itself. Reticles are relatively expensive, so that having to replace a reticle damaged by faulty handling adds cost to the manufacturing process. Accordingly, it is important in microdevice manufacturing to take appropriate steps to ensure that the likelihood of reticle handling faults is minimized.